1. Field of the Invention
This invention has as its object a process for measuring the temperature of a body by optical detection and modulated heating. The process of the invention comes under pyrometry, which is a remote temperature measuring technique.
The process of the invention makes it possible to extend the use of pyrometry to reflecting bodies and to bodies placed in radiating environments. Cases of typical use are:
temperature measurements of objects placed in furnaces, PA1 temperature measurements of reflecting bodies (polished metals, for example).
2. Discussion of Background
Traditional pyrometer runs up against two difficulties which are the following:
(a) the radiation coming from the body whose temperature it is desired to measure is the sum of the radiation emitted by this body and of the radiation reflected by it. Only the radiation emitted by the body depends on the temperature. Therefore, we are bound by a first condition: the reflected flux has to be negligible compared with the emitted flux. It is impossible, for example, to measure the temperature of a very reflecting body or of a body placed in an environment which radiates strongly. This is the case, for example, for polished metals or materials placed in a furnace; PA0 (b) assuming this first problem is solved, there remains a second which is that the amount of radiation detected is proportional to the emitted flux, which is the product of a known function of the temperature (which is the luminance of the ideal blackbody) and of the emissivity of the body studied, which is a characteristic of the sample. Now, this quantity is generally unknown and depends, in particular, on the surface state in the case of solid bodies. PA0 a modulated heating is caused of the zone of the body whose temperature it is desired to measure, PA0 the thermal radiation coming from this zone is detected in at least one wavelength range which provides an electric signal having a continuous component and a modulation component, PA0 the modulation component independent of the reflected fluxes is extracted from the electric signal, this component being a function of the emissivity of the object at the detection wavelength and of the temperature of the body by the derived function in relation to the temperature of the luminance of a blackbody, PA0 by an acquisition and a processing of the appropriate measurements, the temperature of the object is extracted from the modulation component. PA0 the thermal radiation is detected at a first wavelength and at a second wavelength, PA0 for each of these wavelengths, the modulation component--which has the same frequency as the modulation frequency of the heating--is extracted from the signal, this component being proportional to the product of the monochromatic emissivity of the object and of the derivative of the luminance in relation to the temperature, PA0 the ratio of the two components thus obtained is computed for these two wavelengths, this ratio being assumed to be independent of the emissivity of the object and being only a function of the temperature of the body by a function which is the ratio of the derivatives of the luminance in relation to the temperature, PA0 from the value of this ratio, the temperature of the body is computed by inversion of the function in question. PA0 the intensity of the modulated heating is made to vary, PA0 the variation of the modulation component of the electric signal is noted, a variation which comprises a linear term and a quadratic term in relation to the intensity of the modulated heating, PA0 the ratio of these two terms is formed, which no longer depends on the emissivity of the body, strictly in this variant, but on the temperature of the body, PA0 by working at two wavelengths, two ratios R1, R2 are obtained from which ratio R' is formed which depends only on the temperature.
This invention has as its object to overcome these two difficulties.